Hours Veg 18/6 to 24/7 Flower can be 8/16 to 12/12 The most common used
if you are in Flower using HPS then you need more darkness. Some people use both mh and hps for veg but you did not say that.
In veg the warmer the better.. 75-85 if you are running co2 then 85-95 but that is only good for 600w and above which would not help you.
In flower on the colder side after 3 weeks but not below 55. Anything after that the plant will go into stunt mode 99% of the time. Unless you have high altitude strains or cold weather strains
The space heater is good but can be hard to maintain a steady temp if your in a small area. make sure you have an intake and outtake for exhaust. get creative with heat if you need to. just pay attention to the intake and make sure its not coming from something dirty.
Peace out